1. Field of the Invention
The present invention relates to an image heating device using an induction heating system for a device using an electrophotography process, such as an electrophotography copier, an electrostatic printer, or a facsimile.
2. Description of the Related Art
Fixers that fix images to recording materials have been widely used. Such a fixer includes a heating roller having a cylindrical core metal and a release layer provided on the surface of the core metal, and a pressure roller having an elastic layer to press the heating roller. The fixer fixes a toner image to a recording material passing through a nip by heat and pressure with the surface temperature of the heating roller held at a predetermined fixing temperature.
A known example of the heating system of such a heating roller is that a halogen lamp is inserted into the heating roller, and the halogen lamp is turned ON and OFF for holding the temperature of the heating roller at the fixing temperature.
However, with this system, a long rise time is necessary from that the power of the device body is tuned ON to that the surface temperature of the heating roller of the fixer reaches a predetermined fixing temperature.
In addition, since the heat of the halogen lamp indirectly heats the heating roller, the power consumption tends to be increased.
In recent years, a fixer using the induction heating system has been developed. With this heating system, since a fixing roller generates heat due to magnetic flux, the rise time and the heat exchange efficiency are advantageous as compared with those of the halogen system.
For example, a configuration is disclosed in Japanese Patent Publication No. 5-9027. With the configuration, when a high frequency voltage is applied, a coil generates magnetic flux, and a core metal portion of a heating roller made of magnetic ferrous metal generates heat due to the magnetic flux.
Another configuration is disclosed in Japanese Patent No. 02975435 using the induction heating system. With the configuration, the heating roller core metal has a Curie temperature which is almost equal to the fixing temperature. When the temperature of the heating roller core metal reaches the Curie temperature, the core metal loses the magnetic property. Accordingly, the magnetic portion is not increased in temperature, and hence, the magnetic portion can be held at a uniform fixing temperature.
In addition, a coil that defines the heating region has a width larger than the width of a recording material of the maximum size so as to provide the reliable fixing temperature at the edges of the recording material of the maximum size.
However, by determining the width of the coil as described above, regions outside the area corresponding to the width of the recording material of the maximum size are also heated. As a result, resin components such as a gear, and electric components disposed at the end portions of the fixing roller may be heated. This may cause these components to be deteriorated.